Microscopic histologic sections confirming hematopoietic sites.

(A) Microscopic longitudinal section (4 μm) of the proximal ulna showing the transition between BM and cartilage. Hematopoietic cells were found in the BM area. (B) Microscopic section (4 μm) of a 21-week-old fetal temporal skull showing absence of hematopoiesis. Although desmal and enchondral osteosynthesis has taken place in the temporal skull, no hematopoietic cells are found. Also, the other skull bones did not show hematopoietic cells at these gestational ages. Hematoxylin-eosin staining was used.